Numerous methods and devices for determining flow properties of fluid media, i.e., liquids and/or gases, are available. The flow properties may in principle be arbitrary physically and/or chemically measurable properties, which qualify or quantify a flow of the fluid medium. In particular, this may relate to a flow velocity and/or a mass flow rate and/or a volume flow rate. The present invention is described hereafter in particular with reference to so-called hot-film air mass meters, as are described, for example, in Robert Bosch GmbH: Sensoren im Kraftfahrzeug [Sensors in Motor Vehicles], 2007 edition, pages 140-142. Such hot-film air mass meters are typically based on a sensor chip, in particular a silicon sensor chip, having a measuring surface over which the flowing fluid medium may flow. The sensor chip generally includes at least one heating element and at least two temperature sensors, which are situated on the measuring surface of the sensor chip, for example. A mass flow rate and/or volume flow rate of the fluid medium may be inferred from an asymmetry of the temperature profile detected by the temperature sensors, which is influenced by the flow of the fluid medium. Hot-film air mass meters are typically designed as plug-in sensors, which are introducible permanently or replaceably into a flow tube. For example, this flow tube may be an intake manifold of an internal combustion engine.
To be able to precisely infer specific flow properties of the fluid medium from the sensor signals of the hot-film air mass meter, it is desirable in many cases to be able to provide further information about the fluid medium. Thus, for example, a sensor for an internal combustion engine is described in European Patent No. EP 1 017 931 B1, which has an air mass flow meter having a sensor element for detecting the air mass flow taken in. Adjacent to the air mass flow meter and its sensor element, a humidity sensor and a pressure sensor and an analysis circuit for processing the data output by the air mass meter or its sensor element, the humidity sensor, and the pressure sensor are provided and situated in a single housing.
In spite of the technical improvements which are achievable by the device described in European Patent No. EP 1 017 931 B1, in particular the improved signal accuracy and the possibility of determining further properties of the flowing fluid medium, such combined sensors are subject to various technical challenges. These challenges are of a design and production nature in particular. Thus, hot-film air mass meters have been commercially available for many years and are in use in numerous motor vehicles. The integration of pressure and humidity sensors in hot-film air mass meter plug-in sensors, as described in European Patent No. EP 1 017 931 B1, requires an adaptation of the geometry and the design of the plug-in sensor in many cases. Plug-in sensors already in use are therefore not replaceable or are only replaceable with difficulty by new plug-in sensors having pressure and humidity sensors, since in principle the entire module must be replaced. Furthermore, production facilities must be completely converted and reorganized in many cases, as soon as plug-in sensors having additional pressure and humidity measuring capabilities are to be produced. In particular the combined electronic module with a pressure and humidity sensor, as described in European Patent No. EP 1 017 931 B1, requires a substantial adaptation of the production and assembly procedure. In this way, keeping available externally compatible plug-in sensors of different functionalities, i.e., plug-in sensors having pressure and humidity measuring capabilities and plug-in sensors without such pressure and humidity measuring capabilities, is virtually not implementable because of cost concerns. Therefore, a sensor device for detecting a flow property of a fluid medium, which is configured to also generate pressure and temperature signals, and which is producible in a simple and cost-effective way, with the least possible modification of conventional production methods for plug-in sensors without such pressure and humidity measuring capabilities, would be desirable.